This invention relates in general to mechanical pencils, and in particular to a pencil having an exchangeable lead storing container which is releasably coupled to a lead feeding mechanism. The feeding mechanism includes a tubular member with a lead-clamping collet at one end and with a coupling pin at the other end engageable with the storage container, the tubular member being spring-biased into a clamping position and displaceable from the clamping position by an actuation part.
In most cases, conventional mechanical pencils have a lead feeding mechanism which uses a collet for clamping the lead, the collet being operated by means of a pressure knob at the rear end of the pencil or by a similar actuation member. When the pencil is held in an approximately perpendicular position and the feeding mechanism is activated, a lead from the storage container is advanced after a lead being used in the feeding mechanism. Accordingly, the lead storage containers have to be designed in such a manner as to accommodate a plurality of leads and discharge the same one after the other, so that a new lead can be fed through the tip of the pencil when the old lead is consumed. In order to ensure proper functioning of the mechanical pencil, the leads must be easily replaceable, and in addition it is necessary to ensure that the spare leads be transported without trouble from the container to the tip of the pencil.
In the German published patent application No. 28 31 750, a mechanical pencil is described in which spare leads are contained in a capsule in the form of a cylindrical hollow body which at one end thereof is provided with a bottom and at the other end has a removable cap. The leads to be stored in this capsule are shorter than the length of the inner space of the capsule, so that a part of the latter could be used as guiding means for facilitating the insertion of the cylindrical body of the capsule on the lead feeding mechanism. In order to ensure that only those capsules storing leads of a diameter matching the diameter of the lead feeding mechanism be used, the cylindrical member of the feeding mechanism as well as the cylindrical body of the capsule are provided respectively with the same number of guides distributed at uniform spacing so as to permit the insertion of a matching storage capsule only.
Known also are containers for spare leads in the form of cartridges of plastic material having a cylindrical attachment piece connectable to a lead storing container which is firmly built in the mechanical pencil. These containers have the disadvantage that upon the removal of the closure cap the leads are prone to fall out from the cartridge before the latter is plugged into the pencil. Moreover, over, excessive number of leads can be loaded into the pencil from such a cartridge, thus causing wedging of the leads one against the other, and consequently the feeding of the leads into the feeding mechanism is unreliable. This disadvantage has been removed in a lead storing cartridge according to German Gebrauchsmuster No. 77 23 734. This known cartridge has two chambers wherein only a limited number of leads can be stored. It is a disadvantage of this device that, after the removal of the closing gap, there is still the possibility that the leads unintentionally drop out before the cartridge is coupled to the pencil for loading the thin leads. This shortcoming is not removed in any of the prior-art lead storing cartridges.
Also known are ink storing cartridges for fountain pends which are completely sealed and permit the discharge of the writing medium only when a plug-in connection between the cartridge and a container in the fountain pen is established, thus making the operation more comfortable for the user.